Cook Islands

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The Cook Islands｜A Curse in Disguise. The island state could soon become the world's newest developed country. For its leaders, that may not be all good news. Economist, July 21, 2018
https://www.economist.com/asia/2 ... rich-country-status

Note:
(a) Cook Islands
https://en.wikipedia.org/wiki/Cook_Islands
(British Captain James Cook arrived in 1773; most inhabitants are Maori; British protectorate in 1888, British territory in 1990, British Nationality and New Zealand Citizenship Act of 1948, a New Zealand law, grant NZ citizenship to Cook Islanders; a self-governing island country in the South Pacific Ocean in free association with NZ, UN recognition of independence in 1992; has its own currency)

The 2018 CIA World Factbook says its GDP is the same for (both PPP and official exchange rate: "$299.9 million (2016 est.)," and "GDP - per capita (PPP): $16,700 (2016 est.)."
(b) ("At issue is whether the country of 17,000 people has become wealthy enough to warrant a reassignment by the OECD * * * from upper middle-income to high-income status. * * * [Foreign aid was] NZ$33m ($22m) in 2016, or just under 8% of the islands' GDP. * * * The OECD sorts countries into groups based on their gross national income (GNI) per person. Countries that exceed the high-income threshold, as defined by the World Bank, for three consecutive years are promoted to the list of developed countries. (In 2016 the high-income threshold was $12,236.) The Cook Islands, however, does not produce data for GNI, only for GDP, which [the GDP] does not include net income from abroad")

Kimberly Amadeo, Gross National Income. the balance, updated May 15, 2018.
https://www.thebalance.com/gross-national-income-4020738

For all countries, its GDP and GNI are very similar.